Self-assembling micro-ion thrusters: the strange dynamics of superparamagnetic ionic liquids
Anyone with a refrigerator and a prized piece of child’s art has witnessed the impressive external torques and forces that can be transmitted between two magnetized solids. Less obvious to the kitchen observer are the internal forces and torques within each magnet, since these reactions are strongly opposed by the elastic rigidity of the magnetic material and hence the outward shape of each magnet changes imperceptibly. If instead the magnetic material is a fluid then the internal magnetic stresses cause large-amplitude and often surprising rearrangement of the medium. While strongly magnetic fluids do not exist in nature they can be created in the laboratory by dispersing magnetic nanoparticles into a carrier liquid; the resulting colloids are known as ‘ferrofluids.’ In work reported here, novel ferrofluids are synthesized where the carrier fluid is a room-temperature molten salt. The resulting ‘ionic liquid ferrofluids’ are both superparamagnetic and electrically conductive, and thus can be manipulated with both electric and magnetic fields. The dynamics of these exotic fluids will be examined by comparing magneto-electrostatic jets and sprays with their traditional neutral fluid counterparts. A unique application will be introduced wherein an ionic liquid ferrofluid is persuaded to self-assemble into an array of parallel independent electrospray beams useful for spacecraft propulsion.